Prenatal ultrasound imaging

ABSTRACT

An ultrasound system (100) and operating method (200) are disclosed in which the system is adapted to receive a sequence (15) of 2-D ultrasound image frames (150) of a prenatal entity from an ultrasound probe (14) and, for each image frame in said sequence, control the display device to display the received image frame; attempt to segment the image frame for recognition of an anatomical feature of interest (151) of said prenatal entity in said image frame; and accept the image frame for further processing upon recognition of said feature, said further processing comprising: determine a geometric property of the recognized anatomical feature of interest for each accepted image frame; and control the display device to display the determined geometric properties of the accepted image frames in said sequence with each displayed image frame. Such an operating method may be made available as a computer program product for installation on the ultrasound system.

FIELD OF THE INVENTION

The present invention relates to an ultrasound system comprising aprocessor arrangement and a display device under control of theprocessor arrangement, wherein the processor arrangement is adapted toreceive a sequence of 2-D ultrasound image frames of a prenatal entityfrom an ultrasound probe and to control the display device to displaythe received image frames.

The present invention further relates to a method of operating such anultrasound system.

The present invention further relates to a computer program productcomprising a computer readable storage medium having computer readableprogram instructions embodied therewith for, when executed on theprocessor arrangement of such an ultrasound system, cause the processorarrangement to implement such a method.

BACKGROUND OF THE INVENTION

Ultrasonic imaging is routinely used during pregnancy to assess thedevelopment of a prenatal entity, typically a fetus, in the mother'swomb, for example to detect structural anomalies in the fetus. Thetraditional way for a clinician to acquire an image of each requiredview of the prenatal entity is to manipulate an ultrasound probe whilein acoustic contact with the abdomen of the mother until a desiredanatomical orientation is in the plane of the 2D imaging probe. Ifmultiple views are to be generated with such a procedure, for example toimage an anatomical feature of interest of the prenatal entity in itsentirety, the sonographer may move the ultrasound probe over the abdomenof the mother in a particular direction to obtain a temporal sequence of2D image frames.

This for example may be of interest to analyse the development of theprenatal entity, e.g. fetus, using so-called biometry measurements,which are used to check if one or more anatomical features of interestof the prenatal entity are developing correctly, e.g. within expectedtolerances, and/or to estimate gestational age. This may require thesonographer to evaluate each captured image frame in order to performthese measurements, which can be time-consuming. Moreover, if the imageframe sequence is obtained by movement of the ultrasound probe in anon-optimal direction along the mother's abdomen, several of the imageframes may include the anatomical feature of interest in a distortedmanner or may not include the anatomical feature of interest at all.This can make the acquisition of such biometric measurements rathercumbersome and time-consuming.

It is well-known that various fetal anatomical features of interest maybe extracted from a 2D ultrasound image frame using so-called imagesegmentation techniques in which an outline of the anatomical featuresof interest is identified as a segment of the image frame, after whichthe biometric evaluation of the identified feature may be(automatically) performed. For example, Jinhua Yu et al. in Ultrasoundin Med. & Biol. Vol. 34, No. 2, pp 169-182 (2008) disclose a method forfetal abdominal contour extraction and measurement from 2D ultrasoundimage frames, whilst Judith G. Thomas et al. in IEEE Transactions onMedical Imaging, Vol. 10, No. 2 (1991), pages 180-186 disclose theautomatic segmentation of ultrasound images using morphologicaloperators, to name but a few examples of such well-known algorithms.

U.S. Pat. No. 8,891,881 B2 discloses a method for identifying an optimalimage frame. The method includes receiving a selection of an anatomicalregion of interest in an object of interest. Furthermore, the methodincludes obtaining a plurality of image frames corresponding to theselected anatomical region of interest. The method also includesdetermining a real-time indicator corresponding to the plurality ofacquired image frames, wherein the real-time indicator is representativeof quality of an image frame. In addition, the method includescommunicating the real-time indicator to aid in selecting an optimalimage frame. This method therefore may be used to identify the mostpromising image frame for biometric evaluation. However, this methoddoes not aid the sonographer in identifying a suitable direction forultrasound probe movement in order to generate a sufficient number of 2Dimage frames in which a fetal anatomical feature of interest can bereliably recognized.

US 2014/0185895 A1 discloses a computer-implemented method for analyzinga fetal ultrasound image that includes accessing a first statisticalmodel calculated from training data representing shapes of conformingfetal abdominal tissue exemplars and accessing image data representing ascan plane in an ultrasound image. The method further includesidentifying a region of interest including an abdomen in the scan planeusing the first statistical model, accessing a second statistical modelcalculated from training data representing shapes of conforming fetalanatomical structure exemplars, determining whether one or moreanatomical structures are present within the region of interest usingthe second statistical model, and assigning a rating to the scan planebased on the presence of the one or more anatomical structures in theregion of interest.

US 2007/0081705 A1 discloses a method for segmenting and measuringanatomical structures in fetal ultrasound images that includes the stepsof providing a digitized ultrasound image of a fetus comprising aplurality of intensities corresponding to a domain of points on a3-dimensional grid, providing a plurality of classifiers trained todetect anatomical structures in said image of said fetus, and segmentingand measuring an anatomical structure using said image classifiers byapplying said elliptical contour classifiers to said fetal ultrasoundimage, wherein a plurality of 2-dimensional contours characterizing saidanatomical structure are detected.

US 2016/0045152 A1 discloses a method for automatically monitoring fetalhead descent in a birth canal including segmenting each image in one ormore images into a plurality of neighborhood components, determining acost function corresponding to each neighborhood component in theplurality of neighborhood components in each of the one or more images,identifying at least two structures of interest in each image in the oneor more images based on the cost function, wherein the at least twostructures of interest include a pubic ramus and a fetal head, measuringan angle of progression based on the at least two structures ofinterest, and determining the fetal head descent in the birth canalbased on the angle of progression.

SUMMARY OF THE INVENTION

The present invention seeks to provide an ultrasound system that canassist a sonographer in guiding an ultrasound probe in a suitabledirection over a mother's abdominal area to obtain a useful sequence of2D images of the prenatal entity.

The present invention further seeks to provide a method of operatingsuch an ultrasound system.

The present invention still further seeks to provide a computer programproduct comprising a computer readable storage medium having computerreadable program instructions embodied therewith for, when executed onthe processor arrangement of such an ultrasound system, cause theprocessor arrangement to implement such a method.

According to an aspect, there is provided an ultrasound systemcomprising a processor arrangement and a display device under control ofthe processor arrangement, wherein the processor arrangement is adaptedto receive a sequence of 2-D ultrasound image frames of a prenatalentity from an ultrasound probe, said sequence defining a sliding windowof 2-D ultrasound image frames along a translation direction, and, foreach image frame in said sequence, control the display device to displaythe received image frame; attempt to segment the image frame forrecognition of an anatomical feature of interest of said prenatal entityin said image frame; and accept the image frame for further processingupon recognition of said feature, said further processing comprisingdetermine a geometric property of the recognized anatomical feature ofinterest for each accepted image frame; and control the display deviceto display the determined geometric properties of the accepted imageframes in said sequence with each displayed image frame.

In accordance with embodiments of the present invention, the ultrasoundsystem evaluates the respective image frames that it receives from theultrasound probe and attempts to segment the image frames in order toisolate (recognize) an anatomical feature of interest in the imageframes, typically using a suitable segmentation algorithm. Theanatomical feature of interest for example may be selected by a usersuch as a sonographer of the ultrasound system, e.g. using a userinterface or the like. For those image frames for which the segmentationis considered successful by the system, the system keeps track of thegeometric properties of the various accepted image frames and displaysthese geometric properties together with each displayed image frame ofthe sequence, such that for each image frame that is displayed thesonographer is provided with an indication of a spread or variance ofthe obtained geometric properties in the respective image frames of thesequence, thereby providing the sonographer with a clear indication ofthe suitability of the direction in which a sonographer moves theultrasound probe across a region of interest such as an abdominal regionof the mother of the prenatal entity such as a fetus. Consequently, thesonographer is provided with real-time feedback about the suitability ofthe path across which the ultrasound probe is moved by the sonographer,such that the sonographer may alter this path if this feedback isindicative of a sub-optimal path.

Determination of the geometric property may comprise determination of adimension of the recognized anatomical feature such as a diameter orcircumference of the fetal head or abdomen, femur length, nuchaltranslucency, by-parietal diameter, and so on. Any anatomical featurefor which an automatic detection and segmentation algorithm is availablemay be contemplated.

In a preferred embodiment, the processor arrangement is adapted tocalculate a deviation of the determined geometric property from areference value and to control the display device to display eachdetermined geometric property in a manner indicative of a result of saidcalculation. In this manner, a user such as a sonographer gets immediatevisual feedback about the reliability of the determined geometricproperty. For example, in case of an unreliable or potentially spuriousproperty value, the value may be displayed in red whereas in case of areliable property value, this value may be displayed in green such thatthe user can immediately recognize the relevance of a determinedgeometric property of an anatomical feature of interest as identified inthe segmented image frame.

The processor arrangement may be adapted to control the display deviceto display the determined geometric properties of the accepted images insaid sequence in any suitable manner, such as a graph. A graphrepresentation has the advantage that the variance of the determinedgeometric property of time can be recognized in a straightforward mannerby the user.

In an embodiment, the processor arrangement is adapted to control thedisplay device to display an overlay over the recognized anatomicalfeature including the determined geometric property if the displayedimage frame is an accepted image frame such that the user is presentedin real-time with the determined geometric property when the acceptedimage frame corresponding to the determined geometric property isdisplayed on the display device. This for example may include displayingthe overlay in a manner that is indicative of the aforementionedcalculation of the deviation of the determined geometric property fromthe reference value such that the user can readily distinguish betweenreliable values and potentially spurious values.

Preferably, the processor arrangement is further adapted to assesswhether the sequence of images frames as a whole is acceptable. To thisend, the processor arrangement may be adapted to determine a variationin the determined geometric property across the plurality of acceptedimage frames; reject the plurality of accepted image frames if thedetermined variation exceeds a defined threshold; and control thedisplay device to display an indication of said rejection. This providesthe user with feedback information that a particular sequence of imageframes is particularly noisy, such that the user is encouraged torecapture the sequence of image frames by moving the ultrasound probe ina different direction across the region of interest, the choice of whichdirection may be based on captured image frames for which a reliablegeometric property of the anatomical feature of interest could bedetermined.

The processor arrangement may be arranged to make this rejection of theplurality of accepted image frames if the determined variation exceedsthe defined threshold; and a ratio of a total number of accepted imageframes in a complete sequence of image frames and a total number ofimage frames in the complete sequence of image frames is below a definedfurther threshold.

In a preferred embodiment, the ultrasound system further comprises adata storage arrangement, wherein the processor arrangement is adaptedto store the accepted image frames and the determined geometricproperties in the data storage arrangement for evaluation of the imageframes and/or the determined geometric properties at a later point intime, e.g. at any suitable point in time by simple retrieval of theimages from the data storage arrangement, e.g. a memory, for example bymeans of a user interface for selecting one or more images from thesequence.

The ultrasound system does not necessarily include the ultrasound probe,as the ultrasound probe may be external to the ultrasound system, forexample when the ultrasound system comprises implements an ultrasounddiagnosis apparatus to which the ultrasound probe may be attached.Alternatively, the ultrasound system further comprises the ultrasoundprobe, e.g. may form a complete ultrasound imaging system.

In the above embodiments, the sequence of image frames may be a sequenceof 2-D image frames captured by the sonographer moving the ultrasoundprobe over a region of interest as previously explained. However,embodiments of the present invention may be usefully applied to a 3-Dimage, i.e. a volumetric image, wherein the sequence of image framesform part of this volumetric image. In particular, the ultrasound systemmay respond to a user command for slicing the volumetric image in aparticular direction, thereby generating a plurality of 2-D image slices(frames) for which the ultrasound system may attempt to segment eachslice and derive a geometric property of anatomical feature of interestfor successfully segmented slices, and maintain a history of the derivedgeometric properties, which history may provide an indication of thesuitability of the chosen slicing direction in the assessment of aparticular anatomical feature of interest, such that the user of thesystem may use this feedback to choose a different slicing direction inorder to obtain the optimal view of the anatomical feature of interestin the 2-D image slices resulting from the chosen slicing direction.

According to another aspect, there is provided a method for operating anultrasound system comprising a processor arrangement and a displaydevice under control of the processor arrangement, the methodcomprising, with the processor arrangement, receiving a sequence of 2-Dultrasound image frames of a prenatal entity from an ultrasound probe,said sequence defining a sliding window of 2-D ultrasound image framesalong a translation direction, and for each image frame in saidsequence, controlling the display device to display the received imageframe; attempting to segment the image frame for recognition of ananatomical feature of interest of said prenatal entity in said imageframe; and accepting the image frame for further processing uponrecognition of said feature, said further processing comprisingdetermining a geometric property of the recognized anatomical feature ofinterest for each accepted image frame; and controlling the displaydevice to display the determined geometric properties of the acceptedimages in said sequence with each displayed image frame. In this manner,a user of the ultrasound system pertains real-time feedback informationregarding the stability of the geometric property across the sequence ofimage frames, which feedback information may be used by the user toreadjust the direction in which the ultrasound probe is moved across theregion of interest such as an abdominal region of a mother carrying aprenatal entity in order to improve the suitability of the sequence ofimage frames for determining the geometric property of the anatomicalfeature of interest of this prenatal entity.

This may include calculating a deviation of the determined geometricproperty from a reference value and to control the display device todisplay each determined geometric property in a manner indicative of aresult of said calculation to more clearly highlight to the user whethera determined geometric property can be relied on.

In an embodiment, the method further comprises controlling the displaydevice to display an overlay over the recognized anatomical featureincluding the determined geometric property if the displayed image frameis an accepted image frame such that the user gets a real-timeindication of the geometric property, which indication may be used bythe user to readjust the direction in which the ultrasound probe ismoved across the region of interest.

In addition, the method may further comprise determining a variation inthe determined geometric property between the plurality of acceptedimage frames; rejecting the plurality of accepted image frames if thedetermined variation exceeds a defined threshold; and controlling thedisplay device to display an indication of said rejection to aid theuser in determining if the acquired sequence is of sufficient qualityfor evaluating the geometric property of interest of the prenatal entitysuch as a fetus.

According to yet another aspect, there is provided a computer programproduct comprising a computer readable storage medium having computerreadable program instructions embodied therewith for, when executed on aprocessor arrangement of an ultrasound system according to anyembodiment of the present invention, cause the processor arrangement toimplement the method according to any embodiment of the presentinvention. Such a computer program product may be used to augment orotherwise configure the functionality of ultrasound system, e.g. byinstalling the computer readable program instructions on the system.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are described in more detail and by way ofnon-limiting examples with reference to the accompanying drawings,wherein:

FIG. 1 shows a schematic representation of an ultrasound imaging systemin use to scan a part of a patient's body;

FIG. 2 shows a schematic block diagram of an embodiment of an ultrasoundimaging system with an array transducer;

FIG. 3 shows a schematic diagram of the ultrasound imaging apparatus forscanning a fetus;

FIG. 4 shows a schematic diagram of the patient to be scanned in twodifferent viewing directions;

FIG. 5 schematically depicts a sequence of 2-D image frames captured bymoving an ultrasound probe across a region of interest of the patient'sbody;

FIG. 6 is a flowchart of a method of operating an ultrasound systemaccording to an embodiment; and

FIG. 7 schematically depicts a view generated on a display device inaccordance with a method of operating an ultrasound system according toan embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

It should be understood that the Figures are merely schematic and arenot drawn to scale. It should also be understood that the same referencenumerals are used throughout the Figures to indicate the same or similarparts.

FIG. 1 shows a schematic illustration of an ultrasound system 100, inparticular a medical two-dimensional (2D) ultrasound imaging system orthree-dimensional (3D) ultrasound imaging system. The ultrasound system100 may be applied to inspect a volume of an anatomical site, inparticular an anatomical site of a patient 12 over time. The ultrasoundsystem 100 comprises an ultrasound probe 14 having at least onetransducer array having a multitude of transducer elements fortransmitting and/or receiving ultrasound waves. In one example, each ofthe transducer elements can transmit ultrasound waves in form of atleast one transmit impulse of a specific pulse duration, in particular aplurality of subsequent transmit pulses. The transducer elements may bearranged in a linear array in case of a 2D ultrasound system 100 or maybe arranged in a two-dimensional array, in particular for providing amulti-planar or three-dimensional image in case of a 2D ultrasoundsystem 100.

A particular example for a three-dimensional ultrasound system which maybe the CX40 Compact Xtreme ultrasound system sold by the applicant, inparticular together with a X6-1 or X7-2t TEE transducer of the applicantor another transducer using the xMatrix technology of the applicant. Ingeneral, matrix transducer systems as found on Philips iE33 systems ormechanical 3D/4D transducer technology as found, for example, on thePhilips iU22 and HD15 systems may be applied in conjunction with thecurrent invention.

Further, the ultrasound system 100 may comprise a processor arrangementincluding an image reconstruction unit 16 that controls the provision ofa 2D or 3D image sequence via the ultrasound system 100. As will beexplained in further detail below, the image reconstruction unit 16 maycontrol not only the acquisition of data via the transducer array of theultrasound probe 14, but also signal and image processing that form the2D or 3D image sequence out of the echoes of the ultrasound beamsreceived by the transducer array of the ultrasound probe 14.

The ultrasound system 100 may further comprise a display device 18 (fromhere on also referred to as display 18) for displaying the 2D or 3Dimage sequence to the user. Still further, an input device 20 may beprovided that may comprise keys or a keyboard 22 and further inputtingdevices, for example a trackball 24. The input device 20 might beconnected to the display 18 or directly to the image reconstruction unit16.

The ultrasound system 100 may further comprise a data storagearrangement 60, e.g. one or more memory devices, hard disks, opticaldiscs, or the like, in which the image reconstruction unit 16 may storeimage frames and image frame processing data, e.g. for evaluation at alater date, as will be explained in more detail below.

FIG. 2 illustrates a schematic block diagram of the ultrasound system100. The ultrasound probe 14 may, for example, comprise a CMUTtransducer array 26. The transducer array 26 may alternatively comprisepiezoelectric transducer elements formed of materials such as PZT orPVDF. The transducer array 26 is a one- or a two-dimensional array oftransducer elements capable of scanning in two dimensions for 2D imagingor in three dimensions for 3D imaging. The transducer array 26 iscoupled to a microbeamformer 28 in the probe which controls transmissionand reception of signals by the CMUT array cells or piezoelectricelements. Microbeamformers are capable of at least partial beamformingof the signals received by groups or “patches” of transducer elements asdescribed in U.S. Pat. No. 5,997,479 (Savord et al.), U.S. Pat. No.6,013,032 (Savord), and U.S. Pat. No. 6,623,432 (Powers et al.) Themicrobeamformer 28 may be coupled by a probe cable to a transmit/receive(T/R) switch 30 which switches between transmission and reception andprotects the main beamformer 34 from high energy transmit signals when amicrobeamformer 28 is not used and the transducer array 26 is operateddirectly by the main beamformer 34. The transmission of ultrasonic beamsfrom the transducer array 26 under control of the microbeamformer 28 isdirected by a transducer controller 32 coupled to the microbeamformer 28by the T/R switch 30 and the main system beamformer 34, which receivesinput from the user's operation of the user interface or control panel22. One of the functions controlled by the transducer controller 32 isthe direction in which beams are steered and focused. Beams may besteered straight ahead from (orthogonal to) the transducer array 26, orat different angles for a wider field of view. The transducer controller32 can be coupled to control a DC bias control 58 for the CMUT array.The DC bias control 58 sets DC bias voltage(s) that are applied to theCMUT cells.

The partially beamformed signals produced by the microbeamformer 26 onreceive are coupled to the main beamformer 34 where partially beamformedsignals from individual patches of transducer elements are combined intoa fully beamformed signal. For example, the main beamformer 34 may have128 channels, each of which receives a partially beamformed signal froma patch of dozens or hundreds of CMUT transducer cells or piezoelectricelements. In this way the signals received by thousands of transducerelements of the transducer array 26 can contribute efficiently to asingle beamformed signal.

The beamformed signals are coupled to a signal processor 36, which mayform part. The signal processor 36 can process the received echo signalsin various ways, such as bandpass filtering, decimation, I and Qcomponent separation, and harmonic signal separation which acts toseparate linear and nonlinear signals so as to enable the identificationof nonlinear (higher harmonics of the fundamental frequency) echosignals returned from tissue and/or microbubbles comprised in a contrastagent that has been pre-administered to the body of the patient 12. Thesignal processor 36 may also perform additional signal enhancement suchas speckle reduction, signal compounding, and noise elimination. Thebandpass filter in the signal processor 36 can be a tracking filter,with its passband sliding from a higher frequency band to a lowerfrequency band as echo signals are received from increasing depths,thereby rejecting the noise at higher frequencies from greater depthswhere these frequencies are devoid of anatomical information.

The processed signals may be transferred to a B mode processor 38 and aDoppler processor 40. The B mode processor 38 employs detection of anamplitude of the received ultrasound signal for the imaging ofstructures in the body such as the tissue of organs and vessels in thebody. B mode images of structure of the body may be formed in either theharmonic image mode or the fundamental image mode or a combination ofboth as described in U.S. Pat. No. 6,283,919 (Roundhill et al.) and U.S.Pat. No. 6,458,083 (Jago et al.)

The Doppler processor 40 may process temporally distinct signals fromtissue movement and blood flow for the detection of the motion ofsubstances such as the flow of blood cells in the image field. TheDoppler processor 40 typically includes a wall filter with parameterswhich may be set to pass and/or reject echoes returned from selectedtypes of materials in the body. For instance, the wall filter can be setto have a passband characteristic which passes signal of relatively lowamplitude from higher velocity materials while rejecting relativelystrong signals from lower or zero velocity material. This passbandcharacteristic will pass signals from flowing blood while rejectingsignals from nearby stationary or slowing moving objects such as thewall of the heart. An inverse characteristic would pass signals frommoving tissue of the heart while rejecting blood flow signals for whatis referred to as tissue Doppler imaging, detecting and depicting themotion of tissue.

The Doppler processor 40 may receive and process a sequence oftemporally discrete echo signals from different points in an imagefield, the sequence of echoes from a particular point referred to as anensemble. An ensemble of echoes received in rapid succession over arelatively short interval can be used to estimate the Doppler shiftfrequency of flowing blood, with the correspondence of the Dopplerfrequency to velocity indicating the blood flow velocity. An ensemble ofechoes received over a longer period of time is used to estimate thevelocity of slower flowing blood or slowly moving tissue.

The structural and motion signals produced by the B mode and Dopplerprocessors 38, 40 may then be transferred to a scan converter 44 and amultiplanar reformatter 54. The scan converter 44 arranges the echosignals in the spatial relationship from which they were received in adesired image format. For instance, the scan converter 44 may arrangethe echo signal into a two dimensional (2D) sector-shaped format, or apyramidal three dimensional (3D) image. The scan converter 44 canoverlay a B mode structural image with colors corresponding to motion atpoints in the image field with their Doppler-estimated velocities toproduce a color Doppler image which depicts the motion of tissue andblood flow in the image field.

In a 3D imaging system, the multiplanar reformatter 54 will convertechoes which are received from points in a common plane in a volumetricregion of the body into an ultrasonic image of that plane, as describedin US Pat. 6,443,896 (Detmer). A volume renderer 52 converts the echosignals of a 3D data set into a projected 3D image sequence 56 over timeas viewed from a given reference point as described in US Pat. No.6,530,885 (Entrekin et al.). The 3D image sequence 56 is transferredfrom the scan converter 44, multiplanar reformatter 54, and volumerenderer 52 to an image processor 42 for further enhancement, bufferingand temporary storage for display on the display 18.

In addition to being used for imaging, the blood flow values produced bythe Doppler processor 40 and tissue structure information produced bythe B mode processor 38 may be transferred to a quantification processor46 forming part of the processor arrangement. This quantificationprocessor 46 may produce measures of different flow conditions such asthe volume rate of blood flow as well as structural measurements such asthe sizes of organs and gestational age. The quantification processor 46may receive input from the user control panel 22, such as the point inthe anatomy of an image where a measurement is to be made. Output datafrom the quantification processor 46 may be transferred to a graphicsprocessor 50 forming part of the processor arrangement for thereproduction of measurement graphics and values with the image on thedisplay 18. The graphics processor 50 can also generate graphic overlaysfor display with the ultrasound images. These graphic overlays cancontain standard identifying information such as patient name, date andtime of the image, imaging parameters, and the like, as will beexplained in more detail below. For these purposes the graphicsprocessor 50 may receive input from the user interface 22, such aspatient name. The user interface 22 may be coupled to the transmitcontroller 32 to control the generation of ultrasound signals from thetransducer array 26 and hence the images produced by the transducerarray and the ultrasound system. The user interface 22 may also becoupled to the multiplanar reformatter 54 for selection and control ofthe planes of multiple multiplanar reformatted (MPR) images which may beused to perform quantified measures in the image field of the MPR imagesin case of a 3D imaging system.

Again, it shall be noted that the aforementioned ultrasound system 100has only been explained as one possible example for an application ofthe medical ultrasound image processing device 10. It shall be notedthat the aforementioned ultrasound system 100 does not have to compriseall of the components explained before. On the other hand, theultrasound system 100 may also comprise further components, ifnecessary. Still further, it shall be noted that a plurality of theaforementioned components does not necessarily have to be realized ashardware, but may also be realized as software components. A pluralityof the aforementioned components may also be comprised in commonentities or even in one single entity and do not all have to be realizedas separate entities, as this is schematically shown in FIG. 2.

FIG. 3 shows a schematic view of the ultrasound diagnosis apparatuswhich is generally denoted by 10. The ultrasound diagnosis apparatus 10scans by means of the ultrasound probe 14 a fetus, which is generallydenoted by 62. The ultrasound probe 14 scans an anatomical site, whichforms a region of interest and which is generally denoted by 64. Theultrasound probe 14 is connected to the image reconstruction unit 16 viaan ultrasound data interface 66 and which comprises a segmentation unit68, a measurement unit 70 and a calculation unit 72. The imagereconstruction unit 16 is connected to the display 18 for displaying theresults of the ultrasound scan and which is connected to the inputdevice 20 for inputting instructions to control the medical ultrasounddiagnosis apparatus 10.

The segmentation unit 68 is provided for segmenting anatomicalstructures of the fetus 62 in the 3D ultrasound data captured by theultrasound probe 14 and the segmentation unit 68 provides segmentationdata of the anatomical structures of the fetus 62. The measurement unit72 is provided for measuring the anatomical structures of the fetus 62based on the segmentation data provided by the segmentation unit 68. Thecalculation unit 72 is configured to calculate at least one biometricparameter of the fetus 62 based on the segmentation data provided by thesegmentation unit 68. Based on the so-determined at least one biometricparameter, different biometric analyses can be performed, in particularthe gestational age of the fetus 62 can be calculated based on measuredsizes of anatomical structures in the head of the fetus 62.

FIG. 4 shows a detailed schematic diagram of the object 12 to be scannedby the ultrasound probe 14, wherein in this particular case the objectis a fetus 62 to be scanned and to determine a gestational age based onbiometric sizes of different individual biometrical parameter within thehead of the fetus 62.

In order to measure the biometric parameter, at first a plurality ofultrasound scans are performed at different positions with differentregions of interest 64, 64′, as shown in FIG. 4 and the scans areprovided via the ultrasound data interface 66 to the segmentation unit68 in order to perform a model-based segmentation followed by amodel-based measurement.

In the particular case shown in FIG. 4, a calculation of the gestationalage is performed on all different individual biometric measurements,wherein a direct trust correlation of the individual measurements isperformed in order to evaluate an agreement between the measurements ofthe different model-based segmentation measurements. In case of anagreement between the different individual measurements, the accuracy isestimated of the gestational age and all other measurements.

A 3D ultrasound scan typically involves emitting ultrasound waves thatilluminate a particular volume within a body, which may be designated astarget volume or volumetric region. This can be achieved by emittingultrasound waves at multiple different angles. A set of volume data isthen obtained by receiving and processing reflected waves. The set ofvolume data is a representation of the target volume within the bodyover time. Since time is usually denoted as fourth dimension, suchultrasound system 100 delivering a 3D image sequence over time, issometimes also referred to a 4D ultrasound imaging system.

In contrast, in a 2D ultrasound system 100, such a volumetric region istypically created by the sonographer physically moving the ultrasoundprobe 14 over an abdominal region of the mother in order to capture asequence 15 of 2D image frames 150 that may be evaluated by thesonographer to obtain an impression of part of the prenatal entityincluding an anatomical feature of interest 151, as schematicallydepicted in FIG. 5. Such an anatomical feature of interest may be anyanatomical feature that can be automatically recognized in an imageframe 150 by a suitable segmentation algorithm. Such algorithms arewell-known per se and are widely available, such that they will not befurther explained in the present application for the sake of brevityonly. Non-limiting examples of such anatomical features include fetalhead, abdomen, bone structure such as femur or spine, and so on. Thesonographer may be interested in the evaluation of such anatomicalfeatures to determine gestational development, abnormalities, and so on.

Whereas 3D volume data may be re-sliced to give a better viewing anglein case an original viewing angle of the volumetric region did notaccurately display or even failed to display the anatomical feature ofinterest, in 2D imaging the viewing angle is determined by the directionin which the sonographer moves the ultrasound probe 14 over the mother'sabdominal region. However, obtaining the optimal direction in which thesonographer is to move the ultrasound probe 14 over the body region ofinterest (here the mother's abdominal region) is a non-trivial exerciserequiring skill and experience. Consequently, upon acquiring thesequence 15 of 2-D image slices 150, subsequent evaluation of thissequence may indicate that the anatomical feature of interest 151 is notconsistently visible across the sequence 15, e.g. missing from and/ordistorted in at least some of the image slices 151. In such a scenario,the sonographer will need to generate a new sequence 15 of 2-D imageslices 150 by moving, i.e. translating, the ultrasound probe 14 over thebody region of interest in a different direction, in the hope that thisimproves the visibility of the anatomical feature of interest 151 in theimage slices 150. As can be appreciated, this is a trial and errorexercise, which therefore can be rather time-consuming and frustratingfor the sonographer as well as traumatic for the patient.

Embodiments of the present invention seek to provide real-time visualfeedback to a sonographer indicative of the suitability of a sequence 15of 2-D image slices 150 for the evaluation of such an anatomical featureof interest during acquisition of the sequence such that the sonographercan adjust the direction in which he or she moves the ultrasound probe14 across the body region of interest of the patient in accordance withthis visual feedback. To this end, according to one aspect of thepresent invention, the processor arrangement of the ultrasound system100 may be adapted to implement a method 200 of operating the ultrasoundsystem 100 in order to generate such visual feedback, a flowchart ofwhich is shown in Fig.6, which flowchart depicts an example embodimentof this method 200 although it should be understood that variations tothis method, e.g. a variation in the order in which the operationsdepicted in this flowchart are performed, may be contemplated withoutdeparting from the teachings of the present invention.

The processor arrangement may be embodied by a single processor or by aplurality of processors distributed across the ultrasound system aspreviously explained and may be adapted in any suitable manner toimplement the embodiments of the method 200. For example, the desiredfunctionality may be implemented by one or more dedicated hardwarecomponents of the ultrasound imaging apparatus 100, or alternatively maybe realized in software for execution on a suitably configured processorarrangement, e.g. in the form of computer program instructions such asalgorithms that cause such a suitably configured processor arrangementto implement the method 200.

The method 200 starts in operation 201, for example by a sonographercommencing a scan of a patient with the ultrasound probe 14, typicallyby moving, i.e.

translating, the ultrasound probe 14 along a body region of interest ofthe patient such as an abdominal region of a mother carrying a prenatalentity such as a fetus. In operation 203, the processor arrangement,e.g. the image reconstruction unit 16, receives a 2-D image frame 150,preferably with a timestamp 153, from the ultrasound probe 14 andattempts to segment the received image frame in operation 205 using asuitable segmentation algorithm as previously explained in order torecognize an anatomical feature of interest 151 of the prenatal entity.In an embodiment, the ultrasound system 100 may contain a plurality ofsuch segmentation algorithms for recognizing different anatomicalfeatures of interest of such a prenatal entity, in which case thesonographer may select the anatomical feature of interest using the userinterface 20, e.g. by selecting the anatomical feature of interest 151from a selection menu displayed on the display device 18 in operation201 prior to commencing the capturing of the sequence 15.

In operation 207, it is checked if the attempted segmentation of thereceived image frame 150 was successful. If not, the image frame 150 maybe considered as being incorrect or at least unsuitable for theevaluation of the anatomical feature of interest, which may cause themethod 202 proceeds to operation 209 in which the image frame 150 isrejected for further processing. This may further comprise discardingthe image frame 150 although alternatively the rejected image frame 150may be stored in the data storage arrangement 60, e.g. together with arejection indication such that in a later evaluation mode the rejectedimage frame may be immediately recognized as rejected.

On the other hand it is determined in operation 207 that the attemptedsegmentation of the received image frame 150 was successful, the method200 proceeds to 211 in which a geometric property of the recognizedanatomical feature of interest 151 is automatically determined in thesegmented image frame 150, e.g. with the segmentation algorithm. Such ageometric property for example may be a dimension of the geometricfeature of interest 151, e.g. a diameter or circumference of the fetushead or abdominal region, a femur length, nuchal translucency,bi-parietal diameter, and so on, as will be readily understood by theskilled person. The determined geometric property of the recognizedanatomical feature of interest 151 may be stored in the data storagearrangement 60 in operation 213 together with the associated 2-D imageslice 150 and its timestamp 153 for subsequent evaluation, e.g. aninteractive review operation of the sequence 15 as will be explained inmore detail below.

In operation 215, the processor arrangement determines a temporalvariance of the geometric property of the anatomical feature of interest151. To this end, the processor arrangement may maintain a slidingwindow of image frames 150 in which a fixed number of accepted imageframes are kept together with the determined geometric property of theanatomical feature of interest 151 as derived from the segmented imageframes 150 kept in the sliding window. For example, the sliding windowmay be implemented as a buffer of size N, in which N is a positiveinteger of any suitable size, e.g. of size 10. As will be understood bythe skilled person, the choice of the actual value of N is a designchoice which may be made based on a trade-off between accuracy of thevariance estimation and computational effort required to estimate thisvariance. The buffer may form part of the data storage arrangement 60 oralternatively may form part of the processor arrangement, e.g. onon-chip memory such as a cache memory or the like.

The temporal variance may be a variation of the dimension of theanatomical feature of interest 151 across the image frames 150 in thesliding window, or alternatively or additionally may be a variation inthe positioning of the anatomical feature of interest 151 across theimage frames 150, e.g. a change in center of gravity of the anatomicalfeature of interest, which may be indicative of the acquisitiondirection of the sequence 15 of image frames 150 being misaligned with atypical propagation direction of the anatomical feature of interest,which may cause the extracted dimensional of the anatomical feature ofinterest 151 across the image frames 150 to be susceptible toinaccuracy.

The temporal variance in the geometric property of the anatomicalfeature of interest 151 as derived from the sliding window of imageframes 150 is a useful indicator of the stability and therefore thereliability of the sequence 15 of image frames 150 as captured by thesonographer moving the ultrasound probe 14 across the body region ofinterest of the patient under investigation. Therefore, a visualrepresentation of this temporal variance when displaying captured imageframes 150 during the acquisition of the sequence 15 is a usefulindicator to the sonographer of whether the direction in which he or shemoves the ultrasound probe across the body region of interest of thepatient under investigation will lead to a sequence 15 of ultrasoundimage frames 150 from which the geometric property of the anatomicalfeature of interest 151 of the prenatal entity can be reliably obtained.

To this end, in operation 217, the processor arrangement controls thedisplay device 18 such that together with each displayed image frame150, the determined geometric properties of the accepted image frames150 in said sequence 15, e.g. the determined geometric properties of theaccepted image frames 150 in the sliding window, are also displayed,typically such that the temporal variance of these geometric propertiesacross the image frames in the sliding window can be readily recognizedby a sonographer looking at the display device 18. A non-limitingexample of such a displayed image 300 as displayed on the display device18 is schematically depicted in FIG. 7, which image 300 includes the 2-Dimage frame 150, e.g. an accepted 2-D image frame in which theanatomical feature of interest 151 can be recognized by a segmentationalgorithm as previously explained, together with the history 320 ofgeometric properties derived from previously received accepted imageframes 150, e.g. a fixed number of previously received image framesstored in a fixed size buffer implementing a sliding window of suchframes as previously explained. Such a history 320 for example may bedisplayed as a graph or diagram from which a sonographer can immediatelyderive the variation across the historically obtained geometricproperties.

In an embodiment, the processor arrangement is further adapted tocompare each determined geometric property against a reference valuesuch as an expectation value of the geometric property based on thenormal development of the prenatal entity at a certain development stageand to control the display device 18 to display each determinedgeometric property in a manner indicative of a result of thiscomparison. For example, in the history 320, historic geometricproperties 321 falling within a tolerance range of such a referencevalue may be displayed in a manner different to geometric properties 323falling outside this tolerance range such that the sonographer canimmediately assess whether or not most historic geometric properties canbe considered reliable. For example, reliable geometric properties 321may be given a first colour, such as green, whereas unreliable geometricproperties 323 may be given a second colour different to the firstcolour, such as red. Of course, many other distinguishing visualizationsof the geometric properties 321 and 323 will be immediately apparent tothe skilled person. The tolerance range may also be displayed, e.g. as aconfidence interval with upper and lower bounds around each displayedgeometric property to further assist the sonographer in assessing thereliability of the respective geometric properties represented by thehistory 320.

In an embodiment, the processor arrangement is further adapted tocontrol the display device 18 to display the determined geometricproperty of the recognized anatomical feature of interest 151 in anaccepted image frame 150 together with this image frame such that thesonographer is provided with a real-time indication of the geometricproperty of this anatomical feature during acquisition of the sequence15. This may further aid the sonographer the assessment of the prenatalentity under investigation. The determined geometric property may bedisplayed in any suitable manner, for example as an overlay 310 of theassociated image frame 150 displayed on the display device 18. Such anoverlay may be colour-coded based on the comparison of the geometricproperty against the reference value as previously explained, such thata reliable geometric property, e.g. a reliable dimension such as acircumference or diameter, may be readily distinguishable from anunreliable geometric property. For example, a reliable geometricproperty may be shown in green whereas an unreliable geometric propertymay be shown in red although other colours of course may be chosen.Preferably, the same colour coding scheme as used for the history 320 todistinguish between reliable and unreliable values of the geometricproperty is also used for the overlay 310.

At this point it is noted that an image frame 150 rejected in operation209 may also be displayed on the display device 18 together with awarning that the image frame 151 is rejected at least for the purpose ofbiometric measurement acquisition. Such a warning may be any suitablevisible warning, such as a flashing or constantly coloured region on thescreen of the display device 18, an audible warning, and so on.

The method 200 may further evaluate if a sequence 15 of image frames 150as received from the ultrasound probe 14 is sufficiently stable in termsof variance of the geometric property of the anatomical feature ofinterest 151 such that a sonographer can decide whether the sequence 15can be relied upon or whether the sequence 15 needs to be recaptured. Tothis end, the method 200 may check in operation 219 if the acquisitionof the sequence 15 has been completed. This for example may bedetermined based on a user command received from the ultrasound probe 14or the user interface 20 indicative of this completion or based on thesliding window, e.g. the data storage buffer, being full. Other ways ofdetermining whether the sonographer has completed acquisition of asequence 15 will be apparent to the skilled person.

If it is determined in operation 219 that acquisition of the sequence 15of image frames 150 is not yet complete, the method 200 reverts back tooperation 203 in which the next image frame 150 of the sequence 15 isreceived. On the other hand, if it is determined in operation 219 thatacquisition of the sequence 15 is complete, the method 200 proceeds tooperation 221 in which at least the stability and preferably thestability as well as the availability of the anatomical feature ofinterest 151 in the image frames 150 of the sequence 15 is evaluated.For example, the processor arrangement may determine a variation in thedetermined geometric property across the plurality of image frames 150of the sequence 15 accepted in operation 207. Such a variation mayinvolve determining an average value of the geometric property acrossthe plurality of image frames 150 and checking that each image frame 150is associated with a determined geometric property that lies within acertain tolerance range of this average value. Alternatively, this mayinvolve comparing each of the geometric properties against theaforementioned reference value. Other suitable metrics will be apparentto the skilled person. In this manner, it can be determined if thesequence 15 is stable or noisy.

In an embodiment, this determination may be based on a combination ofthe determination of this variance and the ratio of the total number ofaccepted image frames 150 in the sequence 15 and the total number ofimage frames 150 in the sequence 15, i.e. including the image frames 150rejected in operation 207. If this ratio falls below a definedthreshold, this may be a further indication that the sequence 15 isnoisy, such that the sequence 15 may be considered unreliable if atleast one of the variance of the geometric property across the sequence15 is too high and the acceptance rate of image frames 150 in operation207 is too low.

The processor arrangement may control the display device 18 to displaythe evaluation result obtained in operation 221, e.g. by a red light incase of a noisy sequence 15 and by a green light in case of a stablesequence 15. Other distinguishable ways of highlighting the differentoutcomes of this evaluation will be immediately apparent to the skilledperson and may be equally contemplated within the context of theteachings of the present application.

If the sequence 15 of image frames 150 is considered to be noisy inoperation 221, the method 200 may proceed to operation 223 in which thesequence 15 is rejected. Such rejection may be automatic and may causethe removal of the image frames 150 and associated data such as thegeometric property of the anatomical feature of interest 151 in theimage frames 150 from the data storage arrangement 60. Alternatively,the sonographer may be prompted, e.g. by a displayed message on thedisplay device 18, to confirm that the sequence 15 can be removed fromthe data storage arrangement 60. In the latter scenario, the sonographermay decide to keep sequence 15 despite the sequence being considerednoisy, in which case operation 223 may not include deletion of theaccepted image frames 150 of the sequence 15 from the data storagearrangement 60. On the other hand, if the sequence 15 of image frames150 is considered to be stable enough in operation 221, the method 200may proceed directly to operation 225 in which it is determined if thesonographer wish to acquire another sequence 15 of image frames 150.This determination may be made in any suitable manner, for example byresponding to a user instruction provided via the ultrasound probe 14 orthe user interface 20 indicative of the wish to acquire such a furthersequence 15. If this is the case, the method 200 may revert back tooperation 203; otherwise, acquisition of the image frames 150 mayterminate in 227, e.g. the method 200 may enter an interactive reviewmode as will be explained in more detail below.

In this manner, a sonographer is provided with real-time feedbackregarding the reliability and suitability of the sequence 15 of imageframes 150 captured by the sonographer such that a sonographer isprovided with real-time guidance concerning the acquisition of the imageframes 150, which guidance for example may assist the sonographer inguiding the ultrasound probe 14 in an appropriate direction across thebody region of interest of the patient as explained in more detailabove.

However, it should be understood that embodiments of the presentinvention are not limited to the provision of real-time feedback to asonographer. In an embodiment, the data collected with the method 200 asdescribed above may be used in an interactive review mode of theultrasound system 100 in which a sonographer may use the user interface20 to browse through the history of image frames 150 stored in the datastorage arrangement 60 in order to evaluate the recorded image frames150 and associated segmentation information such as the estimatedgeometric property of the anatomical feature of interest 151 recognizedby the segmentation algorithm in the image frame 150. To facilitatenavigation, the processor arrangement for example may cause the displaydevice 18 to display a timeline derived from the timestamps 153 recordedfor each stored image frame 150, such that the sonographer may scrollalong the displayed timeline in order to retrieve an image frame 150corresponding to a particular timestamp from the data storagearrangement 60 and display the retrieved image frame 150 on the displaydevice 18. This may further include the display of the determinedgeometric property of the recognized anatomical feature of interest 151as recognized by the segmentation algorithm in this image frame 150,which geometric property may be displayed in any suitable manner, suchas for example as an overlay as explained in more detail above.Similarly, the segmentation of the image frame 150 may be displayed asan overlay or in any suitable alternative manner as will be immediatelyapparent to the skilled person.

Navigation along such a timeline has the further advantage that thesonographer may identify an image frame 150 in which the anatomicalfeature of interest 151 is particularly well represented, e.g. clearlyvisible without distortions. Based on the timestamp 153 associated withsuch an identified image frame 150, the sonographer may be able toestimate the position of the ultrasound probe 14 on the body region ofinterest in which this image frame was captured, such that the knowledgeof this position may be used by the sonographer to obtain a furthersequence 15 if desired to obtain a further improved clarity orvisibility of the anatomical feature of interest 151 in this furthersequence.

In an embodiment, the processor arrangement may calculate an averagegeometric property for a subset of the stored image frames 150 and causethe display device 18 to display this average geometric property. Such asubset for example may be compiled in response to the selection of aparticular image frame 150 by the sonographer, which subset contains anumber of image frames 150 neighbouring the selected image frame, suchthat a sonographer is presented with an average value of the geometricproperty of interest, e.g. a dimension of the anatomical feature ofinterest 151, which may aid the sonographer in evaluating thisanatomical feature, as it is for instance obviated the need for thesonographer to evaluate a series of individual image frames 150 toobtain this geometric property for a volumetric region of the prenatalentity, e.g. a fetus.

The sonographer may further use this interactive review mode to manuallycorrect determined geometric properties of the anatomical feature ofinterest 151 and/or manually correct proposed segmentations of thestored image frames 150 in order to improve the accuracy of theevaluation of this geometric property if necessary. Where thesonographer manually corrects a proposed segmentation of a stored imageframe 150, the processor arrangement may automatically recalculate thegeometric property of the corrected segmentation of the anatomicalfeature of interest 151. The processor arrangement may further beadapted to automatically update the data storage arrangement 60 with thecorrections made based on the input of the sonographer.

At this point, it is noted that embodiments of the present inventionhave been described in terms of acquisition of 2-D image frames 150 by asonographer manually moving an ultrasound probe 14 across a body regionof interest in a translation direction of the ultrasound probe 14 todefine a sliding window of 2-D image frames 150, each imaging adifferent slice of the fetus 62 . However, it should be understood thatthe principles of the present invention equally may be applied to 3-Dultrasound images in which the sonographer may not have to move theultrasound probe 14 across a body region of interest but in which thesonographer may need to decide in which direction to slice thevolumetric image in order to obtain 2-D image slices corresponding tothe 2-D image frames 150 for further evaluation, e.g. to determine thegeometric property of the anatomical feature of interest 151. In thiscase, the method 200 may evaluate each of the 2-D image slices in orderto determine the stability (variability) of the sequence of image slicesas explained in more detail above such that a sonographer is providedwith real-time feedback about the suitability of the chosen slicingdirection such that a sonographer can obtain guidance as to in whichdirection the volumetric image should be sliced, in which case the slicedirection defines the translation direction in which the sliding windowof image slices is generated, in order to reliably obtain this geometricproperty.

The above described embodiments of the method 200 may be realized bycomputer readable program instructions embodied on a computer readablestorage medium having, when executed on a processor arrangement of theultrasound system 100, cause the processor arrangement to implement themethod 200. Any suitable computer readable storage medium may be usedfor this purpose, such as for example an optically readable medium suchas a CD, DVD or Blu-Ray disc, a magnetically readable medium such as ahard disk, an electronic data storage device such as a memory stick orthe like, and so on. The computer readable storage medium may be amedium that is accessible over a network such as the Internet, such thatthe computer readable program instructions may be accessed over thenetwork. For example, the computer readable storage medium may be anetwork-attached storage device, a storage area network, cloud storageor the like. The computer readable storage medium may be anInternet-accessible service from which the computer readable programinstructions may be obtained. In an embodiment, an ultrasound imagingapparatus is adapted to retrieve the computer readable programinstructions from such a computer readable storage medium and to createa new computer readable storage medium by storing the retrieved computerreadable program instructions in a data storage arrangement, e.g. in amemory device or the like forming part of the data storage arrangement,which data storage arrangement is accessible to the processorarrangement such that the processor arrangement can retrieve thecomputer-readable program instructions from the data storage arrangementfor execution.

It should be noted that the above-mentioned embodiments illustraterather than limit the invention, and that those skilled in the art willbe able to design many alternative embodiments without departing fromthe scope of the appended claims. In the claims, any reference signsplaced between parentheses shall not be construed as limiting the claim.The word “comprising” does not exclude the presence of elements or stepsother than those listed in a claim. The word “a” or “an” preceding anelement does not exclude the presence of a plurality of such elements.The invention can be implemented by means of hardware comprising severaldistinct elements. In the device claim enumerating several means,several of these means can be embodied by one and the same item ofhardware. The mere fact that certain measures are recited in mutuallydifferent dependent claims does not indicate that a combination of thesemeasures cannot be used to advantage.

1. An ultrasound system comprising a processor arrangement and a displaydevice under control of the processor arrangement, wherein the processorarrangement is adapted to: receive a sequence of 2-D ultrasound imageframes of a prenatal entity from an ultrasound probe, said sequencedefining a sliding window of 2-D ultrasound image frames along atranslation direction across said prenatal entity, and, for each imageframe in said sequence: control the display device to display thereceived image frame; attempt to segment the image frame for recognitionof an anatomical feature of interest OM-) of said prenatal entity insaid image frame; and accept the image frame for further processing uponrecognition of said feature, said further processing comprising:determine a geometric property of the recognized anatomical feature ofinterest for each accepted image frame; and control the display deviceto display the determined geometric properties of the accepted imageframes in said sequence with each displayed image frame whereindetermination of the geometric property comprises determination of adimension of the recofnized anatomical feature.
 2. (canceled)
 3. Theultrasound system of claim 1, wherein the processor arrangement isadapted to calculate a deviation of the determined geometric propertyfrom a reference value and to control the display device to display eachdetermined geometric property in a manner indicative of a result of saidcalculation.
 4. The ultrasound system of claim 3, wherein the processorarrangement is adapted to control the display device to display thedetermined geometric properties of the accepted images in said sequenceas a graph.
 5. The ultrasound system of claim 3, wherein the processorarrangement is adapted to control the display device to display anoverlay including the determined geometric property over the recognizedanatomical feature of interest of a displayed accepted image frame. 6.The ultrasound system of claim 1, wherein the processor arrangement isadapted to: determine a variation in the determined geometric propertybetween the plurality of accepted image frames; reject the plurality ofaccepted image frames if the determined variation exceeds a definedthreshold; and control the display device to display an indication ofsaid rejection.
 7. The ultrasound system of claim 6, wherein theprocessor arrangement is adapted to reject the plurality of acceptedimage frames if: the determined variation exceeds the defined threshold;and a ratio of a total number of accepted image frames in a completesequence of image frames and a total number of image frames in thecomplete sequence of image frames is below a defined further threshold.8. The ultrasound system of claim 1, further comprising a data storagearrangement wherein the processor arrangement is adapted to store theaccepted image frames and the determined geometric properties in thedata storage arrangement for evaluation of the image frames and/or thedetermined geometric properties at a later point in time.
 9. Theultrasound system of claim 1, further comprising the ultrasound probe.10. The ultrasound system of claim 1, wherein the sequence of imageframes forms part of a volumetric image.
 11. A method for operating anultrasound system comprising a processor arrangement and a displaydevice under control of the processor arrangement, wherein the methodcomprising, with the processor arrangement: receiving a sequence of 2-Dultrasound image frames of a prenatal entity from an ultrasound probe,said sequence defining a sliding window of 2-D ultrasound image framesalong a translation direction across said prenatal entity, and for eachimage frame in said sequence: controlling the display device to displaythe received image frame; attempting to segment the image frame forrecognition of an anatomical feature of interest of said prenatal entityin said image frame; and accepting the image frame for furtherprocessing upon recognition of said feature, said further processingcomprising: determining a geometric property of the recognizedanatomical feature of interest for each accepted image frame; andcontrolling the display device to display the determined geometricproperties of the accepted images in said sequence with each displayedimage frame, wherein determination of the goemetric property comprisesdetermination of a dimension of the recognized anatomical feature. 12.The method of claim 11, further comprising calculating a deviation ofthe determined geometric property from a reference value and tocontrolling the display device to display each determined geometricproperty in a manner indicative of a result of said calculation.
 13. Themethod of claim 12, further comprising controlling the display device todisplay an overlay including the determined geometric property over therecognized anatomical feature of interest of an accepted image frame.14. The method of claim 11, further comprising: determining a variationin the determined geometric property between the plurality of acceptedimage frames; rejecting the plurality of accepted image frames if thedetermined variation exceeds a defined threshold; and controlling thedisplay device to display an indication of said rejection. 15.(canceled)